1. Field of the Invention
The present invention relates to an acoustic-wave measuring apparatus and an acoustic-wave measuring method. In particular, it relates to an acoustic-wave measuring apparatus that receives acoustic waves generated from a subject irradiated with light, as well as a method for controlling the apparatus.
2. Description of the Related Art
Photoacoustic tomography (PAT) is technique for in-vivo imaging using near-infrared light. In imaging with PAT, a subject, such as a living organism, is irradiated with pulsed light generated from a light source, and the light propagated and spread in the subject is absorbed by a light absorbing substance to generate acoustic waves (typically, ultrasonic waves). The mechanism of the generation of acoustic waves is known as the photoacoustic-wave effect. Tumorous tissue reacts to near-infrared light differently than peripheral tissue, it absorbs light more than the peripheral tissue to expand instantly and generate acoustic waves corresponding to the region that has absorbed the near-infrared light. A photoacoustic imaging apparatus, which is an acoustic-wave measuring apparatus, is an apparatus that receives the acoustic waves with an acoustic-wave detecting element and analyzes the received signal to thereby calculate information, such as spatial initial sound pressure distribution, on acoustic waves generated in the subject and forms an image based on the calculated information. Because the distribution of the generated sound pressure is related to a light absorption coefficient, diagnosis of a subject using the distribution related to the light absorption coefficient is currently being actively studied.
The acoustic-wave measuring apparatus that obtains readings of a living organism using the photoacoustic-wave effect uses a high-output short-pulse (several tens of nanoseconds) light source having a near-infrared wavelength. The near-infrared wavelength band, in which light absorption of living organisms is low, is known as a biological window. Near-infrared light in the biological window can reach deep into living organisms without causing damage. Nevertheless, in an acoustic-wave measuring apparatus using PAT technology it is necessary to prevent the light from irradiating the observer, in particular, the eyes.
To that end, for example, an apparatus described by Manohar, et al., entitled “Region-of-interest breast studies using the Twente Photoacoustic Mammoscope (PAM)”, Proc. of SPIE Vol. 6437 643702, separates the subject and the observer from each other using a blackout curtain.
On the other hand, in order to receive acoustic waves efficiently, it is desirable for the acoustic-wave measuring apparatus to move an acoustic-wave probe, which is an acoustic-wave detecting unit, to a precise predetermined measurement position of the subject and detect the acoustic waves. Furthermore, to generate acoustic waves effectively, it is desirable to move also an irradiation unit that irradiates the subject to the predetermined measurement position and irradiate the subject. For these purposes, the observer must check the measurement position on the subject and move the acoustic-wave probe and the irradiation unit to the desired measurement position. However, since the apparatus described by Manohar, et al., separates the subject and the observer from each other with the blackout curtain, it has a problem in that the observer cannot visually observe the subject and it is difficult to move the irradiation unit to the measurement position with high accuracy. Another measuring method moves the irradiation unit to the measurement position with the blackout curtain opened so as to visually align the irradiation unit with the subject without irradiation of light. In this case, however, the operation of opening and closing the blackout curtain is performed for every measurement, which may often cause the observer to forget to close the blackout curtain or a gap to be generated due to incomplete closing of the blackout curtain.